We have performed long term studies on the effect of mechanical pulmonary ventilation at peak airway pressure of 50 and 30 cm H20 in healthy adult sheep. Following some 24-72 hours of mechanical pulmonary ventilation at those respective peak airway pressures, the total static lung compliance, functional residual capacity, and arterial blood gases gradually deteriorated, leading to adult respiratory distress syndrome (ARDS). From such a point on, recovery with any form of mechanical pulmonary ventilation was no longer possible. However, a similar animal with ARDS when placed on extracorporeal membrane lung bypass and kept on CPAP of 10 cm H20 had a rapid improvement in lung function, great improvement in arterial blood gases, and could be weaned off bypass with long term survival. We conclude that the mechanical pulmonary ventilator at high airway pressures is a major factor in the lack of healing of acutely diseased lungs. The membrane artificial lung can provide for oxygen delivery and CO2 removal without the need for further mechanical pulmonary ventilation; such a course allows for full recovery in diseased lungs.